Conventional prior art exhaust mufflers are elongated
of oval or circular cross-section. These prior art mufflers include a plurality of cylindrical tubes supported in a parallel array by transverse baffles. The baffles typically define an oval or circular shape corresponding to the cross-sectional configuration of the muffler. The tubes and the supporting baffles are disposed within a tubular outer shell which closely engages the baffles, and therefore assumes and defines the oval or circular cross-sectional shape of the muffler. End caps or headers are connected to opposed ends of the tubular outer shell, and short tubular inlet and outlet nipples may be connected to the headers to define the inlet and outlet of the muffler.
The above described prior art muffler construction defines chambers intermediate the baffles and the outer shell of the muffler. Selected portions of the tubes passing through these chambers are perforated, louvered or are provided with other communication means to permit a controlled communication of exhaust gases from the tubes to the chambers of the muffler. Some chambers having perforated tubes passing therethrough are intended to permit the expansion of exhaust gases and/or cross-flow of exhaust gases from one perforated tube to another. Other chambers are provided merely to permit a return flow or change of direction of exhaust gases from one parallel tube to another. Still other chambers are closed end chambers into which a turning tube extends. These closed end chambers are low frequency resonating chambers which cooperate with the respective tuning tubes to attenuate a narrow range of low frequency noise. The dimensions of the tubes, perforations and chambers of the prior art muffler are selected in view of the exhaust gas flow characteristics and to achieve a specified attenuation of the noise associated with the flow of exhaust gas.
The above described conventional prior art mufflers generally perform well. However, they require a large number of separately manufactured components which typically must be assembled in a labor intensive manufacturing process. Mufflers of this type often are excessively heavy in view of the large number of separate components. Additionally, conventional prior art mufflers are relatively limited with respect to the possible sizes and shapes they may assume. Furthermore, designers of exhaust systems are relatively limited with respect to the possible locations for the inlet and outlet nipples and the corresponding alignments for the tail pipe and exhaust pipe leading to or from the conventional prior art muffler. These limitations with respect to the size and shape of the conventional prior art muffler and the alignment of exhaust pipes and tail pipes have become particularly significant in recent years in view of design constraints imposed on the engineers of exhaust systems. In particular, the exhaust system must compete with other vehicular components for the limited available space on the underside of the vehicle.
Mufflers comprising stamp formed components have been available for many years. Stamp formed mufflers have offered the potential for reducing the number of components required for the muffler and have further presented the potential for more automated manufacturing processes. Until recently, most prior art stamp formed mufflers consisted of expansion chambers where perforated tubes passed through a stamp formed chamber of the muffler. Mufflers of this type are functionally limited and generally cannot adequately attenuate all objectionable noise associated with the flow of exhaust gases. Examples of mufflers of this general type are shown in British Patent No. 632,013 which issued to White in 1949; British Patent No. 1,012,463 which issued to Woolgar on Dec. 8, 1965; Japanese Published patent Application No. 59-43456 which was published in 1984; and U.S. Pat. No. 4,132,286 which issued to Hasui et al. on Jan. 2, 1979. U.S. Pat. No. 4,415,059 which issued to Hayashi on Nov. 15, 1983 is a variation of these prior art stamp formed mufflers and shows a straight-through muffler with two short punch formed tuning tubes extending transverse to the through tube. The muffler shown in U.S. Pat. No. 4,415,059 would be functionally very limited, particularly for low frequency noise.
Other prior art stamp formed mufflers have merely included a circuitous array of nonperforated tubes and chambers through which the exhaust gases flow. Prior art stamp mufflers of this general type are shown in U.S. Pat. No. 3,176,791 which issued to Betts et al. on Apr. 6, 1965 and U.S. Pat. No. 3,638,756 which issued to Thiele on Feb. 1, 1972.
Still other prior art stamp formed mufflers include conventional tubular components disposed within a stamped outer shell. Examples of prior art of this type are shown in UK Patent Application No. 21 120 318 and U.S. Pat. No. 4,109,751 which issued to Kabele on Aug. 29, 1978.
U.S. Pat. No. 3,140,755 issued to Tranel on July 14, 1964, and shows a muffler formed from four plates, with a stop-weld material applied to selected surface regions of the plates. The plates are then welded in face-to,-face relationship, and fluid pressure is applied to portions of the plates having the stop-weld thereon. The fluid pressure effectively balloons-out these unwelded portions of the plates. The innermost plates of U.S. Pat. No. 3,140,755 have stop-well selectively located to define a tube that extends through a 180.degree. change in direction and terminates at a location spaced from the periphery of the muffler. The outer plates define a single large chamber surrounding the tube. The end of the chamber opposite the inlet to the muffler is formed to define an outlet. One muffler shown in U.S. Pat. No. 3,140,755 includes a plurality of quarter wave tuning tubes extending orthogonally from the flow tube through the muffler. These quarter wave tuning tubes do not communicate directly with the chamber of the muffler. Another muffler depicted in U.S. Pat. No. 3,140,755 disposes the stop-weld to cause portions of the external shell to be welded to the tube for reinforcement of the external shell. This attachment does not divide the muffler into separate chambers. The single chamber of all mufflers shown in U.S. Pat. No. 3,140,755 would be very limited functionally.
Recently there have been several very significant advances in stamp formed muffler technology disclosed in patents assigned to the assignee of the subject invention. For example, U.S. Pat. No. 4,700,806 issued to Jon Harwood on Oct. 20, 1987 and shows a muffler formed from stamped components and providing the combination of at least one tuning tube and at least one low frequency resonating chamber. The length of the tuning tube extends along the abutting surfaces of the plates from which the tubes are formed. Mufflers manufactured in accordance with U.S. Pat. No. 4,700,806 have proved to be successful in attenuating broad frequency ranges of exhaust gas noise, and have achieved significant commercial success in a relatively short term on the market. U.S. Pat. No. 4,736,817 issued to Jon Harwood on Apr. 12, 1988 as a continuation of the above referenced U.S. Pat. No. 4,700,806. U.S. Pat. No. 4,736,817 shows and claims a muffler having an external shell with a crease formed therein to define a baffle between adjacent chambers of the muffler.
U.S. Pat. No. 4,765,437 issued to Harwood et al. on Aug. 23, 1988 and shows a stamp formed muffler having a pair of formed internal plates defining an array of tubes and a pair of external shells. The muffler shown in U.S. Pat. No. 4,765,437 includes an expansion chamber and a pair of low frequency resonating chambers. The muffler is provided with only one baffle crease formed in each of the external shells. This efficient design facilitates the stamping of the external shell and saves metal as compared to shells having plrral baffle creases.
U.S. Pat. No. 4,821,840 issued to the inventors herein on Apr. 18, 1989 and shows a stamp formed muffler with a conformal outer shell configured to enable the muffler to conform to the shape of the available space on the vehicle.
U.S. Pat. No. 4,860,853 issued to Moring on Aug. 29, 1989 and shows a stamp formed muffler with a non-planar array of tubes. The disclosure of U.S. Pat. No. 4,860,853 explains the several structural and functional advantages afforded by the disclosed design, including a highly reinforced outer shell which eliminates shell ring. Additionally, certain of the embodiments depicted and described in U.S. Pat. No. 4,860,853 provide an extremely efficient muffler with only three stamp formed plates.
Many of the mufflers shown in the above identified patents that are assigned to the assignee of the subject invention are made from a pair of plates that are stamped to define an array of tubes therebetween and at least one external shell having a crease which extends into contact with one of the plates to define a baffle between two chambers of the muffler. The baffle crease in these patents is depicted as extending generally transverse to the direction of the tubes. Thus, the baffle crease includes a nonlinear base with semicircular portions that conform to the cross-sectional shape of the tubes stamp formed in the plates. Additionally, the baffle crease must extend to a depth defined by portions of the adjacent plate intermediate the tubes formed therein. This can require very complex stamp formed configurations for the external shell with considerable drawing and stretching of the metal of the shell. Deep draws of metal as part of stamp forming processes necessarily requires a greater amount of metal with correspondingly high raw material costs and a heavier finished product.
It has been suggested that prior art stamped muffler having a plurality of tubes extending across a baffle crease will necessarily create pockets that can trap moisture or corrosive liquids and lead to a premature failure of the muffler. This alleged potential for corrosion of stamp formed mufflers in the vicinity of pockets defined in the baffle creases has not been observed in tests performed to date. However, a muffler that clearly avoids any such potential for corrosion in the area of the baffle crease is shown in U.S. Pat. No. 4,836,330 which issued to Harwood et al. on June 6, 1989. More particularly, the muffler shown in U.S. Pat. No. 4,836,330 includes only a single tube extending across the baffle crease to avoid the creation of any pockets for trapping moisture in the baffle crease. Although the mufflers shown in U.S. Pat. No. 4,836,330 clearly avoid the potential problem for corrosion in the area of the baffle crease, they still require considerable drawing of metal material.
Another attempt to address the potential problem of corrosion in the vicinity of pockets in the baffle crease of a stamped muffler is shown in U.S. Pat. No. 4,865,154 which issued to Hanson et al. on Sept. 12, 1989. Rather than attempting to avoid the creation of pockets, Hanson provides small drain holes in the areas of the pockets in an effort to permit drainage of any fluids that may accumulate therein. It is believed that any fluids that may accumulate in the pockets of the baffle crease would generally be in the nature of a thick sludge that would quickly clog the drain hole shown in U.S. Pat. No. 4,865,154. Thus, the teaching of U.S. Pat. No. 4,865,154 would appear, at least, to provide only a temporary solution for the alleged problem of corrosion in the vicinity of a baffle crease of a muffler. Furthermore, U.S. Pat. No. 4,865,154 is not effective in reducing the amount of draw of metal in the vicinity of the baffle crease. In fact, several embodiments depicted in U.S. Pat. No. 4,865,154 require even a greater drawing of metal material by providing a flange in one external shell which extends through the aperture defined at the deepest part of the baffle crease.
In view of the above, it is an object of the subject invention to provide a stamp formed muffler which reduces the amount of metal material required to form the external shell of the muffler.
It is another object of the subject invention to provide a stamp formed muffler that provides substantially simpler metal formation in the vicinity of the baffle crease defined in the external shell of the muffler.
It is a further object of the subject invention to provide a stamp formed muffler having a shallower draw of metal for defining the baffle between chambers of the muffler.
It is still an additional object of the subject invention to provide a stamp formed muffler that avoids the creation of pockets in the external shell of the muffler.